Anyone who knows a CrossFitter knows just how rabid the brand's fans can be.

The man behind that brand is Greg Glassman. In 2001, he started his own gym after being "kicked out" of the public gym where he trained clients. That same year, he launched a website and opened his second gym. Those were the humble beginnings of CrossFit.

Thirteen years later, it's a very different story. What started out as one small gym has grown into a $100-million business with 10,000 locations globally -- 40% of which are outside the U.S. -- and 100,000 trainers. It's a trajectory that Mr. Glassman, speaking at Ad Age's Small Agency Conference in Austin, Texas, said was a series of business decisions that weren't exactly rational.

Mr. Glassman is a self-proclaimed "failed academic" with little business sense. "I knew squat about business, but I knew everything about squats," he told the audience at Ad Age's Small Agency Conference in Austin, Texas. But opening up his own gym, he said, made him a businessman.

Despite lacking business acumen, CrossFit over the years developed a brand that has a passionate following. According to Mr. Glassman, it was against all odds. "Our corporate mascot is a vomiting clown," he said. "We're doing everything wrong, but everything's coming out right."

It turns out that Mr. Glassman's strategy was to keep things as simple as possible. Here are some of his so-called "lessons from a rear view mirror" for how to build a passion brand.

Make it about excellence, not about money
"Wanting money isn't enough" to create a strong business, said Mr. Glassman. If money is the aim, the product or service will lack excellence. But if excellence is the aim, it puts the client at the center, and money will come naturally.

Excellence comes from two points, he said: elegance and virtuosity. Elegance for Mr. Glassman was marked by simplicity and efficiency. "Simplicity creates efficiency and eliminates waste," he said. Virtuosity, Mr. Glassman added, was "doing the common uncommonly well. ...These notions have defined excellence and have become the guidepost for everything we do."

Be endearing
CrossFit's path for brand success includes the directive to be endearing. In essence, the client or customer has to love the brand.

But brands "need to endure long enough to make it defining," he said, meaning that brands must offer a product or service so good consumers identify as loyalists to the brand. For example, dedicated CrossFit people identify as CrossFitters; people who ride Harley Davidsons identify as Harley owners. "I know of no brand exception to this process," Mr. Glassman said.

Don't stray too far from the brand mission
"I'm not a business genius but i'm not afraid to make some hard decisions," Mr. Glassman said, which can include leaving some revenue streams alone to keep the brand in focus.

He said that CrossFit could generate an additional $100 million in revenue if it expanded to something like CrossFit-branded supplements or protein shakes. But the point of CrossFit is to offer a quality training program and nothing more. Straying from that purpose "would betray everything I expressed to my community. ...I would betray what I hold dear to get that money," he said.